0 Assigned ID: 7816 ----- Attempting Submission 1 (Thu Apr 16 23:50:07 GMT 2026) ----- HST Phase I Proposal 7816 successfully submitted. Receipt: # 7816-1 ----- Attempting Submission 2 (Thu Apr 16 23:56:46 GMT 2026) ----- HST Phase I Proposal 7816 successfully submitted. Receipt: # 7816-2 ----- Attempting Submission 3 (Thu Apr 16 23:59:19 GMT 2026) ----- 0 ----- Attempting Submission 1 (Tue Aug 18 06:38:29 GMT 2026) ----- Young giant planets encode their formation histories in their accretion history, but recovering accretion rates requires isolating the accretion continuum. The missing piece is UV coverage: only the UV Balmer continuum directly traces Lacc and the shock temperature structure, avoiding the order-of-magnitude uncertainty in current Halpha-based bolometric corrections. We propose consecutive-orbit HST/WFC3/UVIS imaging in F336W and F656N for six wide-orbit planetary-mass companions (3-18 MJup, q~0.005-0.08) spanning BD to K-type hosts. This program will (1) distinguish planetary-shock from magnetospheric accretion; and (2) anchor the LHalpha-Lacc relation across a broad host-mass range, providing the bolometric correction needed for current and upcoming Halpha surveys with MagAO-X, MUSE, and the ELT. We will observe six systems with WFC3/UVIS using two consecutive orbits per system. The primary goals are to measure the Balmer-continuum excess with F336W, H-alpha emission with F656N, and the companion photospheric emission with F555W together with either F775W or F850LP. The bright host stars are intentionally allowed to saturate, and repeated exposures use a three-point dither pattern. The allowed telescope orientation ranges are selected to prevent saturated-host bleeding columns from overlapping the companions while retaining broad scheduling flexibility. ROXs 12, YSES 1, and ITG 15 are observed with F336W, F656N, F555W, and F775W. Their exposure times are designed to detect the companion photosphere at signal-to-noise ratios greater than 5 in both continuum filters. Kointreau-1 and Kointreau-3 are highly extincted, so F336W and F555W are omitted. F850LP provides the photospheric anchor, and the remaining time is assigned to F656N. ROXs 42B has relatively low extinction, but an F555W detection would require too much observing time. We therefore obtain a signal-to-noise ratio greater than 5 in F775W and use the remaining time to strengthen the F336W and especially the F656N constraints. Post-flash levels are selected to produce a total background of approximately 20 electrons per pixel and reduce charge-transfer-efficiency losses. Lillian Jiang (PI) is a PhD candidate at UC Santa Barbara and PI of an HST Cycle 33 program to measure accretion in planetary-mass objects. She has extensive experience with HST, Keck, and JWST observations of young planetary-mass companions, with expertise in UV-optical accretion diagnostics, Halpha emission, and high-contrast imaging. Brendan Bowler is a leading expert in the discovery and characterization of wide-orbit planetary-mass companions and circumplanetary disks, with extensive experience in direct imaging surveys and exoplanet demographics. Michael C. Liu is a pioneer in brown dwarf and exoplanet studies, with deep expertise in infrared observations, spectral characterization, and the physical properties of substellar objects. Claire Finley contributes expertise in the analysis of young planetary-mass companions and accretion diagnostics, including high-contrast imaging and multi-wavelength data reduction. Together, this team combines the observational, technical, and scientific expertise required to obtain and interpret simultaneous UV and Halpha measurements of accreting planetary-mass companions. Exoplanets and Exoplanet Formation Stellar Physics and Stellar Types 6 false false false false false false false SUPPORTED STAR EXTRA-SOLAR PLANETARY SYSTEM LOW MASS COMPANION PRE-MAIN SEQUENCE STAR YSO This object was generated by the targetselector and retrieved from the SIMBAD database. SIMBAD listed proper motion for this target. When retrieving targets with PM from SIMBAD, APT requests the coordinates be calculated with an epoch of the year 2000. Do not modify this epoch. Always review coordinates using the Target Confirmation tool, which graphically displays the PM. XEST-17-036 J2000 J2000 G = 16.52 mag STAR EXTRA-SOLAR PLANETARY SYSTEM LOW MASS COMPANION PRE-MAIN SEQUENCE STAR YSO This object was generated by the targetselector and retrieved from the SIMBAD database. SIMBAD listed proper motion for this target. When retrieving targets with PM from SIMBAD, APT requests the coordinates be calculated with an epoch of the year 2000. Do not modify this epoch. Always review coordinates using the Target Confirmation tool, which graphically displays the PM. ISO-OPH-96 J2000 J2000 R=16.69 mag STAR EXTRA-SOLAR PLANETARY SYSTEM LOW MASS COMPANION This object was generated by the targetselector and retrieved from the SIMBAD database. SIMBAD listed proper motion for this target. When retrieving targets with PM from SIMBAD, APT requests the coordinates be calculated with an epoch of the year 2000. Do not modify this epoch. Always review coordinates using the Target Confirmation tool, which graphically displays the PM. EPIC248030407 J2000 G = 14.98mag STAR EXTRA-SOLAR PLANETARY SYSTEM LOW MASS COMPANION PRE-MAIN SEQUENCE STAR YSO This object was generated by the targetselector and retrieved from the SIMBAD database. SIMBAD listed proper motion for this target. When retrieving targets with PM from SIMBAD, APT requests the coordinates be calculated with an epoch of the year 2000. Do not modify this epoch. Always review coordinates using the Target Confirmation tool, which graphically displays the PM. TYC-8998-760-1 J2000 STAR EXTRA-SOLAR PLANETARY SYSTEM LOW MASS COMPANION PRE-MAIN SEQUENCE STAR This object was generated by the targetselector and retrieved from the SIMBAD database. SIMBAD listed proper motion for this target. When retrieving targets with PM from SIMBAD, APT requests the coordinates be calculated with an epoch of the year 2000. Do not modify this epoch. Always review coordinates using the Target Confirmation tool, which graphically displays the PM. J2000 J2000 STAR EXTRA-SOLAR PLANETARY SYSTEM LOW MASS COMPANION PRE-MAIN SEQUENCE STAR This object was generated by the targetselector and retrieved from the SIMBAD database. SIMBAD listed proper motion for this target. When retrieving targets with PM from SIMBAD, APT requests the coordinates be calculated with an epoch of the year 2000. Do not modify this epoch. Always review coordinates using the Target Confirmation tool, which graphically displays the PM. J2000 J2000 WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F656N WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F656N WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F656N WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F656N WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F656N WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F656N POS-TARG DITHER 0.135 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 1 false /Users/ljiang/Desktop/proposals/HST ideas/Cycle34/1star_planet/phase2/OP-cache/hst_cycle34_18436_6pmc_phase2-v01.xml 1787029968366 The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. KOINTREAU-1 b: two consecutive orbits. Orbit 1 F850LP+F656N; Orbit 2 F656N. F336W and F555W omitted because of high extinction. Saturated primary is intentional. ORIENT ranges for saturated-primary bleed avoidance: 97-257 deg and 277-77 deg. (Tic-Visit :proposal-id 18436 :visit-id "01" :proposal-version -1 :trans-version "20260618" :date "17-Aug-2026 22:12:48.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 41200 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18436 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18436 :visit-id "01" :orbit-number 1 :pcs-time 301 :si-vis-utilization 2678 :al-overhead-at-end 48 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18436 :visit-id "01" :orbit-number 2 :pcs-time 301 :si-vis-utilization 2677 :al-overhead-at-end 48 :internal-dur-at-end 82 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 snr ~ 6.9 /Users/ljiang/Desktop/proposals/HST ideas/Cycle34/1star_planet/phase2/OP-cache/hst_cycle34_18436_6pmc_phase2-v02.xml 1787028637649 The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. KOINTREAU-3 b: two consecutive orbits. Orbit 1 has the three-point F850LP anchor followed by one unpatterned F656N exposure that uses the remaining visibility; Orbit 2 has the three-point F656N sequence. F336W and F555W are omitted because of high extinction. Saturated primary is intentional. ORIENT ranges for saturated-primary bleed avoidance (pending PC approval): 55-215 deg and 235-35 deg (Tic-Visit :proposal-id 18436 :visit-id "02" :proposal-version -1 :trans-version "20260618" :date "17-Aug-2026 21:50:37.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 32048 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18436 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18436 :visit-id "02" :orbit-number 1 :pcs-time 301 :si-vis-utilization 2678 :al-overhead-at-end 48 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18436 :visit-id "02" :orbit-number 2 :pcs-time 301 :si-vis-utilization 2678 :al-overhead-at-end 48 :internal-dur-at-end 72 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 predicted companion S/N ~ 5.1 Additional single F656N exposure using the remaining Orbit 1 visibility /Users/ljiang/Desktop/proposals/HST ideas/Cycle34/1star_planet/phase2/OP-cache/hst_cycle34_18436_6pmc_phase2-v03.xml 1787029530399 The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. ITG 15B: two consecutive orbits. Orbit 1 F336W+F555W; Orbit 2 F656N+F775W. The J-normalized atmosphere predicts F555W S/N about 7.2. Saturated primary is intentional. ETC v34.2 average-background FLASH checks: F336W 560 s FLASH=18 (WFC3UVIS.im.2366577), F555W 225 s FLASH=12 (WFC3UVIS.im.2366568), F656N 746 s FLASH=18 (WFC3UVIS.im.2366578), F775W 25 s FLASH=20 (WFC3UVIS.im.2366570). ORIENT ranges for saturated-primary bleed avoidance: 115-275 deg and 295-95 deg. (Tic-Visit :proposal-id 18436 :visit-id "03" :proposal-version -1 :trans-version "20260618" :date "17-Aug-2026 22:05:30.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 54928 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18436 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18436 :visit-id "03" :orbit-number 1 :pcs-time 301 :si-vis-utilization 2680 :al-overhead-at-end 45 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18436 :visit-id "03" :orbit-number 2 :pcs-time 301 :si-vis-utilization 2682 :al-overhead-at-end 51 :internal-dur-at-end 97 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 2 0 Accretion-continuum exposure; zero-flash background 2.9 e-/pixel. FLASH=18 verified without a CTE warning in WFC3UVIS.im.2366577. Primary saturation allowed. Photospheric anchor; zero-flash background 8.8 e-/pixel. FLASH=12 verified without a CTE warning in WFC3UVIS.im.2366568. J-normalized atmosphere predicts companion S/N about 7.2. H-alpha line exposure; zero-flash background 2.5 e-/pixel. FLASH=18 verified without a CTE warning in WFC3UVIS.im.2366578. Primary saturation allowed. Red photospheric anchor; zero-flash background 0.66 e-/pixel. FLASH=20 verified without a CTE warning in WFC3UVIS.im.2366570. Nominal companion S/N about 24. /Users/ljiang/Desktop/proposals/HST ideas/Cycle34/1star_planet/phase2/OP-cache/hst_cycle34_18436_6pmc_phase2-v04.xml 1787028670754 The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. YSES 1 system: two consecutive orbits; both b and c remain in the subarray. Orbit 1 F336W+F775W; Orbit 2 F656N+F555W. Saturated primary is intentional. ORIENT ranges for saturated-primary bleed avoidance: 359-104 deg, 124-159 deg, 179-284 deg, and 304-339 deg. For companion PAs 214 deg (b) and 159 deg (c), exclude +/-10 deg around ORIENT=169/349 deg and 114/294 deg, respectively; calculation uses the WFC3/UVIS detector-column offset ORIENT=PA+135 deg. (Tic-Visit :proposal-id 18436 :visit-id "04" :proposal-version -1 :trans-version "20260618" :date "17-Aug-2026 21:51:10.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 54928 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18436 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18436 :visit-id "04" :orbit-number 1 :pcs-time 301 :si-vis-utilization 2762 :al-overhead-at-end 50 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3064 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18436 :visit-id "04" :orbit-number 2 :pcs-time 301 :si-vis-utilization 2762 :al-overhead-at-end 49 :internal-dur-at-end 97 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3064 :pcs-gap 0 ) true 2 0 /Users/ljiang/Desktop/proposals/HST ideas/Cycle34/1star_planet/phase2/OP-cache/hst_cycle34_18436_6pmc_phase2-v05.xml 1787030221337 The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. ROXs 12 B: two consecutive orbits. Orbit 1 F336W+F555W; Orbit 2 F656N+F775W. Saturated primary is intentional. ORIENT ranges for saturated-primary bleed avoidance: 17-177 deg and 197-357 deg. (Tic-Visit :proposal-id 18436 :visit-id "05" :proposal-version -1 :trans-version "20260618" :date "17-Aug-2026 22:17:01.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 54928 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18436 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18436 :visit-id "05" :orbit-number 1 :pcs-time 301 :si-vis-utilization 2680 :al-overhead-at-end 45 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18436 :visit-id "05" :orbit-number 2 :pcs-time 301 :si-vis-utilization 2682 :al-overhead-at-end 51 :internal-dur-at-end 97 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2983 :pcs-gap 0 ) true 2 0 predicted companion S/N ~ 5.2. predicted companion S/N about 24. /Users/ljiang/Desktop/proposals/HST ideas/Cycle34/1star_planet/phase2/OP-cache/hst_cycle34_18436_6pmc_phase2-v06.xml 1787028755194 The scheduling data was generated by CASM 34.2. CASM was run in Phase II mode. ROXs 42B b: two consecutive orbits. Orbit 1 F336W+F775W; Orbit 2 is dedicated to F656N. F555W is omitted because a meaningful photospheric detection is too expensive. Saturated primary is intentional. ETC v34.2 average-background FLASH checks: F336W 725 s FLASH=17 (WFC3UVIS.im.2366571), F775W 55 s FLASH=19 (WFC3UVIS.im.2366579), F656N 843 s FLASH=18 (WFC3UVIS.im.2366580). ORIENT ranges for saturated-primary bleed avoidance: 53-213 deg and 233-33 deg. (Tic-Visit :proposal-id 18436 :visit-id "06" :proposal-version -1 :trans-version "20260618" :date "17-Aug-2026 21:52:35.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 41200 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 18436 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 18436 :visit-id "06" :orbit-number 1 :pcs-time 301 :si-vis-utilization 2678 :al-overhead-at-end 50 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) (Tic-Orbit :proposal-id 18436 :visit-id "06" :orbit-number 2 :pcs-time 301 :si-vis-utilization 2677 :al-overhead-at-end 48 :internal-dur-at-end 82 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 2979 :pcs-gap 0 ) true 2 0 Accretion-continuum exposure; zero-flash background 3.8 e-/pixel. FLASH=17 verified without a CTE warning in WFC3UVIS.im.2366571. Red photospheric anchor; zero-flash background 1.5 e-/pixel. FLASH=19 verified without a CTE warning in WFC3UVIS.im.2366579. H-alpha line exposure; zero-flash background 2.8 e-/pixel. FLASH=18 verified without a CTE warning in WFC3UVIS.im.2366580.